Lime-with-Bite Cupcakes

You can't tell from the picture, but these cupcakes are TART. Almost too tart for me. I made them for my friend James' birthday, and James loves citrus with a bite -- I made him tart lemon cupcakes a couple of years ago, and now it was time to try lime. The trick is, there aren't really any recipes out there for extra-tart lime baked goods other than key lime pie. So I had to figure it out myself. The lemon ones I did a couple of years ago were also no good as a starting point -- I'd used a doctored cake mix family recipe, and no one makes lime cake mix.

So I found a recipe from Cook's Illustrated that used a good deal of lemon zest and juice in the batter, and substituted lime. I used a little bit more zest than it called for, too, since lime is generally a subtler flavor than lemon.


The cake was good, but nowhere near tart. So once the cupcakes came out of the oven, I poked holes in them with a toothpick and poured a little glaze over, glaze made of lime juice with a little sugar. That made the cakes about as tart as I could get them without making like a million test batches -- I don't want to mess with the chemistry of baking that much.


But it's the frosting where you can really get zingy. There's a lot less chemistry in frosting -- with American buttercream, it's just a matter of tweaking for taste and consistency. So this frosting is really, really tart. James loved it, as did a lot of my friends. If I were making this again for myself (and I probably will, because I love lime), I would make it a good deal less tart, because that's my preference.


One other note - I had planned to fill these cupcakes with lime curd, but I ran out of time. So I incorporated some of the lime curd into the frosting. I've done this before, and I love the flavor of it. It's probably not strictly necessary, but lime curd is SO GOOD that I like putting it everywhere.


Lime-with-Bite Cupcakes
adapted from Cook's Illustrated
makes 24 cupcakes

For cake:
3 tablespoons lime juice (from about 2 large limes)
2 tablespoons lime zest (from about 2 large limes)
3 cups unbleached all-purpose flour
1 teaspoon baking powder
1/2 teaspoon baking soda
1 teaspoon salt
1 teaspoon vanilla extract
3/4 cup buttermilk
3 large eggs, at room temperature
1 large egg yolk, at room temperature
18 tablespoons (2-1/4 sticks) unsalted butter, at room temperature
2 cups sugar

For glaze:
3 tablespoons lime juice
1 tablespoon sugar

1. Adjust oven rack to lower-middle position; heat oven to 350 degrees. Line cupcake tins with papers.
   
2. Mince lime zest to fine paste (you should have about 2 tablespoons). Combine zest and lime juice in small bowl; set aside to soften, 10 to 15 minutes.
3. Whisk flour, baking powder, baking soda, and salt in large bowl. Combine lime juice mixture, vanilla, and buttermilk in medium bowl. In small bowl, gently whisk eggs and yolk to combine.
   
4. In standing mixer fitted with flat beater, cream butter and sugar at medium-high speed until pale and fluffy, about 3 minutes; scrape down sides of bowl with rubber spatula. Reduce to medium speed and add half of eggs, mixing until incorporated, about 15 seconds. Repeat with remaining eggs; scrape down bowl again.
   
5. Reduce to low speed; add about one-third of flour mixture, followed by half of buttermilk mixture, mixing until just incorporated after each addition (about 5 seconds). Repeat using half of remaining flour mixture and all of remaining buttermilk mixture. Scrape bowl and add remaining flour mixture; mix at medium-low speed until batter is thoroughly combined, about 15 seconds. Remove bowl from mixer and fold batter once or twice with rubber spatula to incorporate any remaining flour. Scrape into prepared pan.
6. Bake until tops are golden brown and wooden skewer or toothpick inserted into center comes out with no crumbs attached, about 20 minutes.
7. Let cool 5 minutes, still in pan. While cooling, mix together 1 tablespoon sugar and 3 tablespoons lime juice. (I stuck mine in the microwave for about 20 seconds to get the sugar to dissolve.)
8. Poke holes in the cupcakes with a toothpick or skewer. Pour about 1 teaspoon of glaze over each cupcake, while the cupcakes are still hot.

Lime Curd
adapted from Martha Stewart, via chockylit's Cupcake Bakeshop

4 large egg yolks
2/3 cup sugar
5 tablespoons freshly squeezed lime juice, strained
1/2 teaspoons gelatin
5 tablespoons unsalted butter, cut into small pieces
7 tablespoons heavy cream
2 teaspoons powdered sugar

1. In a small bowl, sprinkle gelatin over 1/2 tablespoon lime juice. Let sit.
2. Whisk together egg yolks, sugar, and citrus juice in a small, heavy-bottomed saucepan. Cook over low heat, stirring constantly, until mixture coats the back of a spoon, about 4 minutes.
   
3. Remove from heat. Immediately stir in gelatin mixture. Stir in butter, piece by piece. Pour through fine-mesh sieve into a small bowl. Cover with plastic wrap (press the wrap onto the surface of the curd), and cool in the refrigerator until cold, at least 2 hours.
   
4. Whip together cream and powdered sugar until stiff peaks form. Fold cream into the chilled curd.

Tart Lime Frosting
makes more than enough for 24 cupcakes

1 cup (2 sticks) unsalted butter, room temperature
2 pounds confectioner's sugar
1/2 recipe lime curd (above)
approx. 1 cup lime juice
approx. 14 small TrueLime packets(optional)

1. In the bowl of a standing mixer, beat the butter until soft. Add about 1/2 pound of confectioner's sugar. Beat until incorporated.
   
2. Add some lime curd (approx 1/2 cup). Beat until incorporated.
   
3. Add some lime juice (approx 2 tablespoons). Beat until incorporated.
4. Add approx. 1/2 pound more confectioner's sugar. Beat until incorporated.
5. Keep adding lime curd, lime juice, and confectioner's sugar until the consistency is where you want it.
6. If you want to bring the TART, add TrueLime packets until your mouth puckers.